1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a printer.
2. Description of the Related Art
A plurality of ink ejection nozzles designed to eject the same ejection amount practically eject different ejection amounts due to manufacturing variations. Accordingly, when the plurality of ejection nozzles are used to form an image on a printing medium with the number of uniform printing dots, a density variation due to the manufacturing variations and the like may occur. Japanese Patent Laid-Open No. H10-013674 (1998) discloses a head shading technique that, in order to settle the density variation, acquires information on ink amounts ejected from respective ink ejection nozzles, and according to the information on ink amounts, modulates the number of printing dots.
Meanwhile, even in the case of using the head shading technique as described above, when two or more inks are superimposed to perform color reproduction, a phenomenon in which color development in a region where printing is performed with nozzles having different ejection amounts from a standard one is different from a color that should have been printed, i.e., a so-called color shift occurs. That is, only by the head shading technique, even if density unevenness of a single color image is corrected, on an image expressed by superimposing two or more inks, the color shift may occur according to a variation in ejection characteristic among a plurality of nozzles. If the ejection characteristic is different among the plurality of nozzles, a degree of the color shift is different between printed regions, and this is recognized as color unevenness.
When colorimetry of the occurrence site of such color unevenness is performed with a colorimeter, a colorimetric error may occur. For example, a spectrophotometric colorimeter performs the colorimetry by reading reflected light within a certain spot diameter. However, color unevenness in a region having a width smaller than the spot diameter, up to in a region surrounding the color unevenness, is read by the spectrophotometric colorimeter. For this reason, it is difficult to accurately perform the colorimetry of the color unevenness. Also, in the case of an image input device such as a scanner, there are some cases where metamerism occurs depending on a degree of accuracy of a sensor, where color difference cannot be discriminated depending on the number of bits upon generation of an input image, and others, i.e., human visual accuracy may not be reproducible.